U.S. Pat. No. 6,424,288 invented by Daniel L. Woodell and assigned to the assignee of the present application discloses a system for and methods of displaying radar information using weather radar systems. Weather radar systems generally include an antenna, a receiver/transmitter circuit, a processor, and display. The processor is coupled between the display and the receiver/transmitter circuit. The receiver/transmitter circuit is coupled between the processor and the antenna.
The processor provides transmit signals through the receiver/transmitter circuit to the antenna to transmit radar beams. The processor receives radar return signals derived from radar returns received by the antenna. The radar return signals are provided to the processor via the receiver/transmitter circuit.
Conventionally, pilots use weather radar systems to detect and avoid hazardous weather. The radar return signals are processed to provide graphical images to a radar display. The radar display is typically a color display providing graphical images in color to represent the severity of weather. Some aircraft weather radar systems also include other hazard detection systems such as a turbulence detection system. The turbulence detection system can provide indications of the presence of turbulence or other hazards. Conventional weather radar systems include those manufactured by Rockwell Collins, Inc., Honeywell International, Inc. and others.
An article entitled “The Vertical Profile of Radar Reflectivity of Convective Cells: A Strong Indicator of Storm Intensity And Lightning Probability?” by Zipser and Lutz, Monthly Weather Review (August 1994, vol. 122, pp. 1751–1759) discusses the use of reflectivity data from Doppler radars and temperature readings to determine a lightning hazard. U.S. Pat. No. 6,405,134 discloses a system and method for predicting areas where lightning strikes are likely to occur by evaluating radar data and temperature data.
The system uses radar data associated with radar composite reflectivity. Weather can be particularly problematic as an aircraft approaches the terminal area. Operation near the terminal area (takeoff and approach) are critical periods of flight in which an aircraft moves only a few tens of knots above stall speed. Accordingly, turbulent environments, gust conditions and lightning can be particularly hazardous during an aircraft's takeoff and approach.
Radial wind gusts can cause the air speed of the aircraft to momentarily fall below stall speed with the resulting momentary attitude upset and possible hazardous loss of control. Radial wind gusts are wind gusts that are directed toward or away from the heading of an aircraft. Wind gusts perpendicular to the aircraft velocity cause yaw attitude disturbances and force the aircraft off the proper ground track for the approach or takeoff. Aircraft pilot's manuals recommend increasing approach and takeoff airspeed in terminal areas where gust conditions are present.
Generally, aircraft approach speeds are selected to provide a 30–50 knot (15–26M/S) margin above stall speed. When gust conditions are detected or reported along the approach path, speed is increased according to aircraft pilot's manuals to provide additional margin. For small general aviation or regional aircraft, the amount of speed increase is approximately equal to the peak gust speed. For larger air transport aircraft that have higher overall approach speeds, the amount of speed increase may be less. For example, the pilot may only be interested in peak gusts exceeding 10 knots in larger transport aircraft.
Pilots conventionally receive information about gust conditions through forecasts prior to takeoff, through pilot reports, or through ground-based instruments relayed through air-traffic control. Forecasts and pilot reports can be disadvantageous because they can be out-of-date and unreliable as fast moving storm systems move through the airport terminal area. Ground-based instruments, such as ground-based gust detection systems, can only provide approximate estimates of gust magnitudes at higher altitudes associated with the approach and takeoff.
With respect to lightning hazards, aircraft operating in terminal areas conventionally come closer to convective activity or convective weather cells than while in a cruise mode. Operating near convective activity may induce a lightning strike that can cause a maintenance action and even ground the aircraft. Total avoidance of convective activity is not an option in the terminal area because the aircraft must depart and land in coordination with other aircraft. In the terminal area, aircrafts generally follow the following rule: If the aircraft in front of my aircraft successfully departs or land through a weather cell, my aircraft will as well.
Lightning sensors have been designed for aircraft. However, NASA studies have shown that 90% of lightning strikes on aircraft are induced by the aircraft itself as it travels through an electrified environment and that lightning strikes are not often the result of a lightning bolt randomly hitting the aircraft. The NASA studies also show that 60% of all lightning strikes on an aircraft had neither visually detectable lightning before nor after the recorded strike on the aircraft. Accordingly, while a lightning detector may be a good identifier of a convective cell over a longer length of time, a lightning sensor cannot guarantee timely detection of a potential lightning strike in the short exposure time associated with terminal areas.
Applicants believe that the large number of strikes without either a precursor or subsequent strike can be understood in light of aircraft actively avoiding regions of high level radar reflectivity that occur during both the early and mature stages of a thunderstorm's development. Aircraft begin to operate in the vicinity of cells during the dissipating stages of a thunderstorm's life as radar reflectivity falls. Although the dissipating reflectivity may seem insufficient to denote an electrified cell, the cell has been charged earlier in its life. The aircraft penetrating the environment near the dissipating but still charged cell may act as a trigger to allow the cell to discharge through the aircraft.
This phenomenon highlights the need to identify cells and their stages of development. There is a need to identify a potential lightning producing cell, often a cell that needs to be identified as a risk even after it no longer meets the hazard triggering thresholds for some period of time.
Thus, there is a need for a system for and a method of predicting hazards in the terminal area using a weather radar system. Further still, there is a need for real time or pseudo-real time hazards determination using an aircraft weather radar system. Yet further, there is a need for a weather radar system optimized to determine the potential for lightning and/or wind gusts. Yet further still, there is a need for a system that automatically detects gust strength and lightning potential so that a pilot can more accurately avoid hazardous conditions in a terminal area. There is also a need for a weather radar system that can determine and display lightning and/or wind gust hazards. Even further, there is a need for a weather radar system that can identify potential lightning hazard areas.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.